Plan B’s European version, Norlevo, is getting an alert that warns the emergency contraceptive may not be as effective in heavier women.

The decision by European regulators is based on a study conducted in 2011 by researchers at the University of Edinburgh that found women with a body mass index (BMI) greater than 25 who used levonorgestrel, which prevents pregnancy following intercourse, had a four times greater chance of becoming pregnant than those with lower BMIs. Here’s what family-planning and research experts say you need to know about the morning after option.

Is Europe’s Norlevo the same as the U.S.’s Plan B?
Yes, both contain the same amount of levonogestrel, which is a progestin that blocks the release of the egg from the ovary or prevents fertilization of the egg by sperm.

Why did the European regulators decide to add warnings about weight to Norlevo’s label?
European regulators decided that the evidence from the Scottish study was enough to inform users of Norlevo of the possible effect that weight could have on the drug’s ability to prevent pregnancy. Norlevo’s maker, HRA Pharma, conducted its own research and realized its product was not effective in preventing pregnancy in women weighing more than 176 lb., according to CNN. HRA Pharma then submitted a request to the regulating body for a change in its label, and the organization approved the alteration, which will take effect in 2014.

Will the U.S. Food and Drug Administration (FDA) add the same information to Plan B?
The FDA is currently reviewing existing data to decide whether to change the drug’s label, as well as the labels of other similar drugs currently available in the U.S. But some reproductive-health experts note that there isn’t much data on how weight affects levonogestrel, so there may not be enough evidence to justify any action by the FDA. “I don’t necessarily think it’s inevitable that the FDA would act on this,” says Dr. Carolyn Westhoff, professor of obstetrics and gynecology and public health at Columbia University and senior medical adviser at Planned Parenthood Federation of America. “People in the field have been scratching their heads since [the 2011 study] was published, saying what sorts of studies could we do to get more data to help us understand this better. To my knowledge, nobody has done those additional studies.”

Is Plan B unsafe?
There is no harm from the health perspective, but if the product is not effective in preventing pregnancy in certain women, who expect it to do so, that poses different types of harms, say family-planning experts.

Should women who weigh more than 176 lb. avoid Plan B if they don’t want to get pregnant?
Plan B, which is made by Teva Pharmaceuticals, is just one form of emergency contraception. Both ella and the copper IUD are more effective in preventing pregnancy – ella is effective for up to five days after unprotected sex while Plan B must be used within 72 hours of intercourse.